Cast components are often designed to the limit of their mechanical properties to take advantage of strength to weight ratios. The requirement for more stringent emissions is also a contributing factor due to seeking high combustion pressures and temperatures. Because of the physical characteristics of cast materials, specifically gray cast iron in engine applications, the thermal fatigue limit is often reached causing failure in certain areas of the component. When this happens, it is difficult and time consuming to repair castings and other components often resulting in significant downtime and costs for the component owner. Typically repairs to castings involve removing damaged portions of the casting through machining, and subsequently rebuilding the damaged area by welding.
An example of a component that is susceptible to damage is the cylinder head of an internal combustion engine. Because of repeated heating and cooling of the engine, the cylinder heads often reach their thermal fatigue limit and develop cracks near openings, such as valve seats, fuel injector bores, and exhaust ports. Another problem associated with cylinder heads is warping. When warped, the bottom surface of the head becomes uneven and does not seal properly. Some warped cylinder heads can be milled until the fireside surface is again flat. However, milling the surface reduces the thickness of the head, making the head more susceptible to future operating damage. Heads that can't be milled flat are typically scrapped.
One example of producing a casting having localized areas of improved thermal resistance of the cylinder head is U.S. Pat. No. 4,337,736 (the'736 patent) issued to Raush et al. The '736 patent discloses a cast iron cylinder head having a preformed workpiece of a thermal fatigue-resistant alloy material metallically bonded to the cylinder head around the valve bridge area to provide reinforcement in this area. The preformed workpiece has thin fusible sections, which melt when the hot base material is cast over them. Although the disclosure of the '736 patent may provide for localized areas of improved thermal resistance, it may be costly and have limited applicability.
The present disclosure is directed to overcoming one more of the problems set forth above.